全文获取类型
收费全文 | 18365篇 |
免费 | 148篇 |
国内免费 | 9篇 |
专业分类
林业 | 3765篇 |
农学 | 1403篇 |
基础科学 | 177篇 |
3200篇 | |
综合类 | 842篇 |
农作物 | 2378篇 |
水产渔业 | 1986篇 |
畜牧兽医 | 1499篇 |
园艺 | 1181篇 |
植物保护 | 2091篇 |
出版年
2023年 | 23篇 |
2022年 | 77篇 |
2021年 | 90篇 |
2020年 | 99篇 |
2019年 | 139篇 |
2018年 | 2854篇 |
2017年 | 2811篇 |
2016年 | 1307篇 |
2015年 | 143篇 |
2014年 | 109篇 |
2013年 | 250篇 |
2012年 | 902篇 |
2011年 | 2238篇 |
2010年 | 2179篇 |
2009年 | 1310篇 |
2008年 | 1426篇 |
2007年 | 1634篇 |
2006年 | 77篇 |
2005年 | 135篇 |
2004年 | 133篇 |
2003年 | 183篇 |
2002年 | 83篇 |
2001年 | 21篇 |
2000年 | 67篇 |
1999年 | 16篇 |
1998年 | 15篇 |
1997年 | 12篇 |
1996年 | 16篇 |
1995年 | 15篇 |
1994年 | 11篇 |
1993年 | 16篇 |
1992年 | 15篇 |
1991年 | 6篇 |
1990年 | 9篇 |
1989年 | 11篇 |
1988年 | 14篇 |
1987年 | 8篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 9篇 |
1983年 | 4篇 |
1981年 | 4篇 |
1979年 | 5篇 |
1977年 | 5篇 |
1975年 | 3篇 |
1973年 | 3篇 |
1972年 | 3篇 |
1971年 | 3篇 |
1968年 | 5篇 |
1967年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Huimin Yang Murray Unkovich Ann McNeill Xianzhi Wang 《Biology and Fertility of Soils》2011,47(4):377-385
Symbiotic N2 fixation by lucerne (Medicago sativa) has capacity to provide significant inputs of N to agro-ecosystems, and the species has also been shown to scavenge soil
mineral N and thus act as a sink for excess reactive N. The balance between these two N cycle processes was investigated in
an extensive irrigated lucerne growing region where nitrate contamination of groundwater has been reported. We sampled 18
permanent pure lucerne stands under irrigation for standing dry matter, total shoot N, and N2 fixation using 15N natural abundance along with activity of the inducible enzyme nitrate reductase as indicators of use of soil NO3− by lucerne. On average 65% of lucerne N was obtained from symbiotic N2 fixation. Converting standing dry matter estimates to annual N2 fixation amounts we calculated average N2 fixation of 311 kg N/ha, including N in roots and nodules. Uptake of N from soil by lucerne was calculated to be 181 kg N/ha/year.
We were not able to identify the source of this soil mineral N, although nitrate reductase activity of lucerne was higher
than that of non-N2 fixing species examined. 相似文献
42.
43.
44.
Umma Tamima 《林业研究》2016,27(4):853-861
The objective was to evaluate the performance of the co-management of Nishorgo Support Project at Chunati Wildlife Sanctuary in Bangladesh. I adopted the Focus Groups Discussion method for opinion survey and applied the SWOTAHP technique for data analysis. Local people did not participate in the decision-making process of forest management and they perceived co-management as a threat to their livelihoods. Moreover, mistrust and misunderstanding among different stakeholders, political and ethical conflicts, lack of property rights of tribal communities, and lack of accountability and transparency were identified as the drawbacks of co-management. 相似文献
45.
The present investigation was conducted to assess the ameliorative effects of foliar‐applied trehalose on growth, photosynthetic attributes, water relation parameters and oxidative defence mechanism in two maize cultivars under field water deficit conditions. Various components of the experiment comprised two maize cultivars (EV‐1098 and Agaiti‐2002), two water‐stress levels (irrigation after 2 weeks and irrigation after 3 weeks during the entire period of growth), and two levels of trehalose (0 and 30 mm ) and four replicates of each treatment. Water stress significantly reduced the plant biomass production, photosynthetic attributes and water relation parameters in both maize cultivars. In contrast, water stress considerably increased the leaf malondialdehyde (MDA) contents, the activities of antioxidant enzymes such as peroxidase (POD), superoxide dismutase (SOD) and catalase (CAT), and the levels of non‐enzymatic compounds such as ascorbic acid and tocopherols. In contrast, water stress caused a marked reduction in leaf phenolic contents. Foliar‐applied trehalose significantly increased plant biomass production, and improved some key photosynthetic attributes and plant–water relation parameters. The ameliorative effect of exogenously applied trehalose was also observed on the activities of some key antioxidant enzymes (POD and CAT) and non‐enzymatic compounds (tocopherols and phenolics). Overall, exogenously applied trehalose considerably improved drought tolerance of maize plants by up‐regulating photosynthetic and water relation attributes as well as antioxidant defence mechanism. 相似文献
46.
47.
48.
49.
50.